In general, a small-sized camera module is mounted in mobile terminals such as a smartphone. As such a camera module, a lens driving device (for example PTL 1) is employed. The lens driving device has an auto focus function of automatically performing focusing for capturing a subject (hereinafter referred to as “AF (Auto Focus) function”), and a shake correction function (hereinafter referred to as “OIS (Optical Image Stabilization) function”) of optically correcting hand shake (vibration) upon capturing an image to reduce the irregularities of the image.
The auto-focusing and shake-correcting lens driving device includes an auto-focusing driving part (hereinafter referred to as “AF driving part”) for moving the lens part in the light axis direction, and a shake-correcting driving part (hereinafter referred to as “OIS driving part”) for swaying the lens part in a plane orthogonal to the light axis direction.
The AF driving part includes, for example, an auto-focusing coil part (hereinafter referred to as “AF coil part”) disposed around the lens part, and an auto-focusing magnet part (hereinafter referred to as “AF magnet part”) disposed separately from the AF coil part in the radial direction. An auto-focusing movable part (hereinafter referred to as “AF movable part”) including the lens part and the AF coil part is moved with respect to an auto-focusing fixing part (hereinafter referred to as “AF fixing part”) including the AF magnet part in the light axis direction by use of a driving force of a voice coil motor composed of the AF coil part and the AF magnet part, and thus focusing is automatically performed. In the following, the AF movable part and the AF fixing part are collectively referred to as “auto-focusing unit (AF unit).”
Here, a lens position for bringing a subject at a smallest capture distance (a position on the most light reception side) into focus is called “macro position,” and a lens position for bringing a subject at the infinity (a position on the most imaging side) into focus is called “infinity position.” That is, the range from the macro position to the infinity position is the movable range of the AF movable part.
The OIS driving part includes, for example, an OIS magnet part disposed in the AF unit, and an OIS coil part disposed separately from the OIS magnet part in the light axis direction. The OIS movable part (the AF unit and the OIS magnet part) is supported by a supporting member separately from the OIS fixing part (OIS coil part) in the light axis direction. The OIS movable part is swayed in a plane orthogonal to the light axis direction by use of a driving force of a voice coil motor composed of the OIS magnet part and the OIS coil part, and thus shake correction is performed.
The OIS magnet part may also serve as the AF magnet part, and with such a configuration, the size and the height of the lens driving device can be reduced.
In the lens driving device disclosed in PTL 1, an elastic supporting part (an upper leaf spring and a lower leaf spring) connects a lens holder (as a part of the AF movable part) in which the AF coil part is disposed at the outer peripheral surface, with a magnet holder (as a part of AF fixing part) in which the AF magnet part (also serve as the OIS magnet part) is disposed. At the time of focusing, the AF movable part moves in the light axis direction until the driving force (driving power) of the voice coil motor of the AF driving part and the restoration force of the elastic supporting part are equivalent to each other, and the AF movable part is held in that state. Accordingly, a driving force corresponding to the restoration force of the lower leaf spring and the upper leaf spring in the maximum displacement state is required for the voice coil motor of the AF driving part.
In addition, in the lens driving device disclosed in PTL 1, a spacer is disposed to the lower leaf spring on the imaging side in order to limit the movement of the AF movable part toward the imaging side in the light axis direction. Thus, in the lens driving device disclosed in PTL 1, in an non-energization state where focusing is not performed, the AF movable part is biased, with the back tension of the upper leaf spring and the lower leaf spring, to the spacer side and is brought to the closest position (see FIG. 2 of PTL 1). That is, the AF movable part is held at the infinity position in a non-energization state where focusing is not performed, and is moved toward the macro position in an energization state where focusing is performed.